Multiple-loop refrigeration systems are widely used for the liquefaction of gases at low temperatures. In the liquefaction of natural gas, for example, two or three closed-loop refrigeration systems may be integrated to provide refrigeration in successively lower temperature ranges to cool and liquefy the feed gas. Typically, at least one of these closed-loop refrigeration systems uses a multi-component or mixed refrigerant which provides refrigeration in a selected temperature range as the liquid mixed refrigerant vaporizes and cools the feed gas by indirect heat transfer. Systems using two mixed refrigerant systems are well-known, in some applications, a third refrigerant system using a pure component refrigerant such as propane provides initial cooling of the feed gas. This third refrigerant system also may be used to provide a portion of the cooling to condense one or both of the mixed refrigerants after compression. Refrigeration in the lowest temperature range may be provided by a gas expander loop that is integrated with a mixed refrigerant loop operating in a higher temperature range.
In a typical multi-loop mixed refrigerant process for liquefying natural gas, the low level or coldest refrigeration loop provides refrigeration by vaporization in a temperature range of xe2x88x9230 to xe2x88x92165xc2x0 C. to provide final liquefaction and optional subcooling of cooled feed gas. The refrigerant is completely vaporized in the coldest temperature range and may be returned directly to the refrigerant compressor, for example, as described in representative U.S. Pat. Nos. 6,119,479 and 6,253,574 B1. Alternatively, the completely vaporized refrigerant may warmed before compression to provide precooling of the feed gas as described in U.S. Pat. Nos. 4,274,849 and 4,755,200 or for cooling of refrigerant streams as described in Australian Patent AU-A-43943/85. A common characteristic feature of these typical liquefaction processes is that the refrigerant in the low level or coldest refrigeration loop is completely vaporized while providing refrigeration in the lowest temperature range. Any additional refrigeration provided by the refrigerant prior to compression thus is effected by the transfer of sensible heat from the vaporized refrigerant to other process streams.
In known liquefaction processes that use three integrated closed-loop refrigeration systems, the size of the process equipment in the third or lowest temperature refrigeration system may be smaller relative to the two warmer refrigeration systems. As the process liquefaction capacity is increased, the sizes of the compression and heat exchange equipment in the two warmer systems will reach the maximum sizes available from equipment vendors, while the sizes of the corresponding equipment in the lowest temperature refrigeration system will be smaller than the maximum sizes. In order to further increase the production capacity of this liquefaction process, parallel trains would be needed because of compression and/or heat exchanger size limitations in the two warmer refrigeration systems.
It would be desirable to increase the maximum production capacity of this liquefaction process at the limits of available compressor and heat exchanger sizes, thereby allowing the use of larger single-train liquefaction processes. This need is addressed by the present invention, which provides an integrated refrigeration system having increased production capacity without requiring duplicate parallel equipment for the warmer refrigeration systems.
In one embodiment, the invention relates to a method for liquefying a gas which comprises cooling a feed gas stream successively through first and second temperature ranges to provide a liquefied product, wherein refrigeration for cooling the feed gas stream in the first temperature range is provided by a first vaporizing refrigerant and refrigeration for cooling the stream in the second temperature range is provided by a second vaporizing refrigerant, and further wherein the second vaporizing refrigerant provides additional refrigeration by vaporization at temperatures above a lowest temperature in the first temperature range.
In another embodiment, the invention relates to a method for liquefying a gas which comprises cooling a feed gas stream (1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream in the first temperature range is provided by a first vaporizing refrigerant (117), refrigeration for cooling the stream in the second temperature range is provided by a second vaporizing refrigerant (213), and refrigeration for cooling the stream in the third temperature range is provided by a third vaporizing refrigerant (315), and further wherein the third vaporizing refrigerant provides additional refrigeration by vaporization (317) at temperatures above a lowest temperature in the second temperature range.
The first temperature range may be between 35 and xe2x88x9270xc2x0 C., the second temperature range may be between 0 and xe2x88x92140xc2x0 C., and the third temperature range may be between xe2x88x9290 and xe2x88x92165xc2x0 C. The feed gas stream (1) may be natural gas.
The cooling of the feed gas stream (1) may be effected by:
(a) cooling the feed gas stream (1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101);
(b) further cooling the partially cooled feed stream (5) in the second temperature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and
(c) further cooling the second partially cooled feed stream (9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316).
Another embodiment of the invention relates to a method for liquefying a gas which comprises cooling a feed gas stream (1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream is provided by a first refrigerant (117) vaporizing in the first temperature range, a second refrigerant (213) vaporizing in the second temperature range, and a third refrigerant (315) vaporizing in the third temperature range and further vaporizing at temperatures above a lowest temperature in the second temperature range, wherein the cooling of the feed gas stream (1) is effected by:
(a) cooling the feed gas stream (1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101);
(b) further cooling the partially cooled feed stream (5) in the second temperature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and
(c) further cooling the second partially cooled feed stream (9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316);
wherein the third refrigerant (315) may be a multi-component mixture comprising two or more components selected from the group consisting of nitrogen and hydrocarbons having from one to five carbon atoms and the third refrigerant may comprise (in mole %) 5-15% nitrogen, 30-60% methane, 10-30% ethane, 0-10% propane, and 5-15% i-pentane. The third refrigerant may comprise i-pentane and one or more hydrocarbons having four carbon atoms, wherein the molar ratio of i-pentane to the one or more hydrocarbons having four carbon atoms is greater than one. The third refrigerant may comprise i-pentane and n-pentane and the molar ratio of i-pentane to n-pentane in the third refrigerant may be greater than one.
An alternative embodiment of the invention relates to a method for liquefying a gas which comprises cooling a feed gas stream (1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream is provided by a first refrigerant (117) vaporizing in the first temperature range, a second refrigerant (213) vaporizing in the second temperature range, and a third refrigerant (315) vaporizing in the third temperature range and further vaporizing at temperatures above a lowest temperature in the second temperature range, wherein the cooling of the feed gas stream (1) is effected by:
(a) cooling the feed gas stream (1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101);
(b) further cooling the partially cooled feed stream (5) in the second temperature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and
(c) further cooling the second partially cooled feed stream (9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316);
wherein the third refrigerant (315) is a multi-component mixture comprising two or more components selected from the group consisting of nitrogen and hydrocarbons having from one to five carbon atoms, wherein the third refrigerant comprises i-pentane and n-pentane and wherein the molar ratio of i-pentane to n-pentane in the third refrigerant is greater than one, and wherein the i-pentane and n-pentane may be obtained from the feed gas stream and the molar ratio of i-pentane to n-pentane in the third refrigerant may be greater than the molar ratio of i-pentane to n-pentane in the feed gas stream.
Another alternative embodiment of the invention relates to method for liquefying a gas which comprises cooling a feed gas stream (1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream is provided for by a first refrigerant (117) vaporizing in the first temperature range, a second refrigerant (213) vaporizing in the second temperature range, and a third refrigerant (315) vaporizing in the third temperature range and further vaporizing at temperatures above a lowest temperature in the second temperature range, wherein the cooling of the feed gas stream (1) is effected by:
(a) cooling in the feed gas stream (1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101);
(b) further cooling the partially cooled feed stream (5) in the second temperature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and
(c) further cooling the second partially cooled feed stream (9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316);
wherein the third refrigerant (315) is a multi-component mixture comprising two or more components selected from the group consisting of nitrogen and hydrocarbons having from one to five carbon atoms, and wherein the third refrigerant may comprise i-pentane and one or more hydrocarbons having four carbon atoms, wherein the i-pentane and one or more hydrocarbons having four carbon atoms in the third refrigerant may be obtained from the feed gas stream, and wherein the molar ratio of i-pentane to the one or more hydrocarbons having four carbon atoms in the third refrigerant may be greater than the molar ratio of i-pentane to the one or more hydrocarbons having four carbon atoms in the feed gas stream.
A further embodiment of the invention includes a method for liquefying a gas which comprises cooling a feed gas stream (1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream is provided by a first refrigerant (117) vaporizing in the first temperature range, a second refrigerant (213) vaporizing in the second temperature range, and a third refrigerant (315) vaporizing in the third temperature range and furhter vaporizing at temperatures above a lowest temperature in the second temperature range, wherein the cooling of the feed gas stream (1) is effected by:
(a) cooling the feed gas stream (1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101);
(b) further cooling the partially cooled feed stream (5) in the second temperature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and
(c) further cooling the second partially cooled feed stream (9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316);
and wherein the third refrigerant (315) may be provided in a third recirculating refrigeration process that comprises vaporizing the two-phase refrigerant stream (316) in a fourth heat exchange zone (317) at temperatures greater than a lowest temperature in the second temperature range to provide a third refrigerant vapor (318), compressing (319, 324) the third refrigerant vapor (318) to yield a compressed third refrigerant stream (328), cooling the compressed third refrigerant stream (328) in the fourth heat exchange zone (317) by indirect heat exchange with the two-phase refrigerant stream (316) to provide a cooled third refrigerant stream (329), and further cooling the cooled third refrigerant (329) stream to provide the third refrigerant (315) in (c).
The further cooling of the cooled third refrigerant stream (329) may be effected by indirect heat exchange with the third refrigerant (315) vaporizing in the third heat exchange zone (312). The compressed third refrigerant stream (328) may be provided by compressing the third refrigerant vapor (318) in a first compression stage (319) to provide a first compressed vapor, cooling (320) the first compressed vapor to yield a two-phase stream, separating (321) the two-phase stream into a vapor stream (322) and a liquid stream (323), compressing the vapor stream (322) to yield a further compressed vapor, pumping (325) the liquid stream (323) to provide a pressurized liquid, combining the further compressed vapor and the pressurized liquid to yield a combined refrigerant stream (326), and cooling the combined refrigerant stream (326) to provide the compressed third refrigerant stream (328).
Another embodiment of the invention includes a method for liquefying a gas which comprises cooling a feed gas stream (1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream is provided by a first refrigerant (117) vaporizing in the first temperature range, a second refrigerant (213) vaporizing in the second temperature range, and a third refrigerant (315) vaporizing in the third temperature range and further vaporizing at temperatures above a lowest temperature in the second temperature range, wherein the cooling of the feed gas stream (1) is effected by:
(a) cooling the feed gas stream (1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101);
(b) further cooling the partially cooled feed stream (5) in the second temperature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and
(c) further cooling the second partially cooled feed stream (9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316);
and wherein the third refrigerant (315) may be provided in a third recirculating refrigeration process that comprises vaporizing the two-phase refrigerant stream (316) in a fourth heat exchange zone (355) at temperatures greater than a lowest temperature in the second temperature range to provide a third refrigerant vapor (348), compressing (349) and cooling (350) the third refrigerant vapor (348) to yield a compressed third refrigerant stream (351), cooling the compressed third refrigerant stream (351) in the first heat exchange zone (353) by indirect heat exchange (352) with the first vaporizing refrigerant (117) and in the fourth heat exchange zone (355) by indirect heat exchange with the vaporizing two-phase refrigerant stream (316) to provide a cooled third refrigerant stream (329), and further cooling the cooled third refrigerant stream (329) to provide the third refrigerant (315) in (c).
Other embodiments of the invention include a method for liquefying a gas which comprises cooling a feed gas stream (1) successively through first, second, and third temperature ranges to provide a liquefied product (13), wherein refrigeration for cooling the feed gas stream is provided by a first refrigerant (117) vaporizing in the first temperature range, a second refrigerant (213) vaporizing in the second temperature range, and a third refrigerant (315) vaporizing in the third temperature range and further vaporizing at temperatures above a lowest temperature in the second temperature range, wherein the cooling of the feed gas stream (1) is effected by:
(a) cooling the feed gas stream (1) in the first temperature range by indirect heat exchange with the first refrigerant (117) vaporizing in a first heat exchange zone (310) to provide a first partially cooled feed stream (5) and a first refrigerant vapor (101);
(b) further cooling the partially cooled feed stream (5) in the second temperature range by indirect heat exchange with the second refrigerant (213) vaporizing in a second heat exchange zone (311) to provide a second partially cooled feed stream (9) and a second refrigerant vapor (201); and
(c) further cooling the second partially cooled feed stream (9) in the third temperature range by indirect heat exchange with the third refrigerant (315) vaporizing in a third heat exchange zone (312) to provide the liquefied product (13) and a two-phase refrigerant stream (316);
and wherein the third refrigerant (315) may be provided in a third recirculating refrigeration process that comprises combining the two-phase refrigerant stream (316) with a cooled reduced-pressure liquid refrigerant stream to provide a combined two-phase refrigerant stream (347), vaporizing the combined refrigerant stream (347) in a fourth heat exchange zone (344) at temperatures greater than a lowest temperature in the second temperature range to provide a third refrigerant vapor (330), compressing (331) and cooling (332) the third refrigerant vapor (330) to provide a partially-condensed third refrigerant, separating (333) the partially-condensed third refrigerant into a refrigerant vapor stream (334) and a refrigerant liquid stream (335), compressing (336) and cooling (337) the refrigerant vapor stream (334) to form a partially-condensed stream and separating (338) the partly-condensed stream into a compressed third refrigerant vapor (339) and a liquid refrigerant (340), reducing the pressure (341) of the liquid refrigerant to provide a reduced-pressure liquid refrigerant (342), combining the reduced-pressure liquid refrigerant (342) with the refrigerant liquid stream (335) to provide a combined refrigerant liquid (343), subcooling the combined refrigerant liquid stream (343) in the fourth heat exchange zone (344) to provide a subcooled liquid refrigerant, combining the subcooled liquid refrigerant and the two-phase refrigerant stream (316) to provide a combined two-phase refrigerant (347), vaporizing the combined two-phase refrigerant (347) in the fourth heat exchange zone (344) to provide refrigeration therein, cooling compressed third refrigerant vapor (339) in the fourth heat exchange zone (344) to provide a cooled third refrigerant stream (329), and further cooling (356) and reducing the pressure (314) of the cooled third refrigerant stream (329) to provide the third refrigerant (315).
Another embodiment of the invention relates to a system for liquefying a gas stream which comprises first (310), second (311), and third (312) heat exchange zones for cooling the gas stream successively through first, second, and third temperature ranges, respectively, to provide a liquefied product, a first refrigeration system for providing a first refrigerant in a first refrigerant line (117) to the first heat exchange zone (310), a second refrigeration system for providing a second refrigerant in a second refrigerant line (213) to the second heat exchange zone (311), and a third refrigeration system for providing a third refrigerant in a third refrigerant line (315) to the third heat exchange zone (312), wherein the third refrigeration system comprises piping means (318) to provide a vaporized third refrigerant to compression means for compressing the vaporized third refrigerant, piping means (328) to provide a compressed third refrigerant to a fourth heat exchange zone (317), piping means (329) for providing a cooled compressed third refrigerant from the fourth heat exchange zone (317) to the third heat exchange zone (312), means to further cool (356) the cooled compressed third refrigerant in the third heat exchange zone (312) to provide a condensed third refrigerant, and pressure reduction means (314) to reduce the pressure of the condensed third refrigerant to provide the third refrigerant to the third refrigerant line (315) and the third heat exchange zone (312).
The compression means for compressing the vaporized third refrigerant may comprise a first stage compressor (319), an intercooler (320) to cool and partially condense a first compressed refrigerant stream to yield a partially condensed first compressed refrigerant stream, a separator (321) to separate the partially condensed first compressed refrigerant stream into a vapor refrigerant stream and a liquid refrigerant stream, a second stage compressor (324) to compress the vapor refrigerant stream to provide a compressed vapor refrigerant stream, a pump (325) to pressurize the liquid refrigerant stream to provide a pressurized liquid refrigerant stream, piping means (326) to combine the compressed vapor refrigerant stream and the pressurized liquid refrigerant stream and provide a combined refrigerant stream to an aftercooler (327) to cool the combined refrigerant stream to provide the compressed third refrigerant.
The fourth heat exchange zone (344) may include means for subcooling a refrigerant liquid to provide a subcooled refrigerant liquid, pressure reduction means (346) for reducing the pressure of the subcooled refrigerant liquid to provide a reduced-pressure refrigerant, piping means (347) for combining the reduced-pressure refrigerant with the further vaporizing third refrigerant from the third heat exchange zone (312) to provide a combined vaporizing refrigerant stream to the fourth heat zone (344), wherein the combined vaporizing refrigerant stream vaporizes in the fourth heat exchange zone (344) to provide the vaporized third refrigerant.
The compression means for compressing the vaporized third refrigerant may comprise a first stage compressor (331), an intercooler (332) to cool and partially condense a first compressed refrigerant stream to yield a partially condensed first compressed refrigerant stream, a first separator (333) to separate the partially condensed first compressed refrigerant stream into a first vapor refrigerant stream and a first liquid refrigerant stream, a second stage compressor (336) to compress the vapor refrigerant stream to provide a compressed vapor refrigerant stream, an aftercooler (337) to cool the compressed vapor refrigerant stream to provide a cooled two-phase refrigerant stream, a second separator (338) to provide a second liquid refrigerant stream and the compressed third refrigerant, pressure reduction means (341) to reduce the pressure of the second liquid refrigerant stream to provide a reduced-pressure second liquid refrigerant stream, and piping means (335, 342, 343) to combine the reduced-pressure second liquid refrigerant stream and the first liquid refrigerant stream to provide the refrigerant liquid to the fourth heat exchange zone (344).
In another embodiment, the invention relates to a system for liquefying a gas stream which comprises first (353), second (311), and third (312) heat exchange zones for cooling the gas stream successively through first, second, and third temperature ranges, respectively, to provide a liquefied product, a first refrigeration system for providing a first refrigerant vaporizing in the first heat exchange zone (353), a second refrigeration system for providing a second refrigerant vaporizing in the second heat exchange zone (311), and a third refrigeration system for providing a third refrigerant vaporizing in the third heat exchange zone (312), wherein the third refrigeration system comprises compression means (349) for compressing a vaporized third refrigerant to provide a compressed third refrigerant, cooling means (352) in the first heat exchange zone (353) for cooling the compressed third refrigerant by indirect heat exchange with the first refrigerant vaporizing in the first heat exchange zone (353) to provide a cooled compressed third refrigerant, a fourth heat exchange zone (355) to further cool the cooled compressed third refrigerant by indirect heat exchange with a vaporizing third refrigerant from the third heat exchange zone (312) to provide the vaporized third refrigerant and a further cooled compressed third refrigerant, means to further cool (356) the cooled compressed third refrigerant in the third heat exchange zone (312) to provide a condensed third refrigerant, and pressure reduction means (314) to reduce the pressure of the condensed third refrigerant to provide the third refrigerant vaporizing in the third heat exchange zone (312).
In a related embodiment, the invention includes a refrigerant comprising i-pentane, one or more hydrocarbons having four carbon atoms, and one or more components selected from the group consisting of nitrogen, methane, ethane, ethylene, propane, and propylene, wherein the molar ratio of i-pentane to the one or more hydrocarbons having four carbon atoms is greater than one. The refrigerant also may contain n-pentane and the molar ratio of i-pentane to n-pentane may be greater than one.
An embodiment of the invention also relates to a refrigerant comprising i-pentane, one or more hydrocarbons having four carbon atoms, and one or more components selected from the group consisting of nitrogen, methane, ethane, ethylene, propane, and propylene, wherein the molar ratio of i-pentane to the one or more hydrocarbons having four carbon atoms is greater than one, and wherein the refrigerant may have a composition comprising (in mole %) 5-15% nitrogen, 30-60% methane, 10-30% ethane, 0-10% propane, and 5-15% i-pentane.